1. Field of the Invention
The present invention relates to a vehicle-mounted device communication controller, and more particularly to a vehicle-mounted device communication controller capable of searching the existence of portable units promptly and with a high degree of accuracy by sending/receiving signals between a vehicle-mounted unit and a plurality of portable units.
2. Description of the Related Art
Conventionally, for vehicle-mounted device communication controllers which are used mounted in automotive vehicles, the controllers having a passive keyless entry function have been known. A vehicle-mounted device communication controller of this type is provided with a vehicle-mounted unit, and necessary information is exchanged by the communication using radio signals between the vehicle-mounted unit and one or more portable unit to be carried by the user. As an example of the communication performed at this time, the vehicle-mounted unit sends a low-frequency radio signal to each of the portable units as a search signal intermittently, when any one of the portable units receives this search signal, the received portable unit sends back a response signal, and when the vehicle-mounted unit receives this response signal, the communication is established between the vehicle-mounted unit and the portable unit. Then when the communication is established between the vehicle-mounted unit and the portable unit, the vehicle-mounted unit authenticates the portable unit, which is the communication opponent, that the portable unit is an ID registered normal portable unit. After such an authentication is performed, in the vehicle-mounted device communication controller, the passive keyless entry system changes the setting of the door-locking mechanism from a lock state to an unlock state in order to enable the user (vehicle operator) and the like to open the door freely.
In this regard, the communication performed between the vehicle-mounted unit and the portable unit is carried out timely after the setting of the door-locking mechanism have having changed, and the checking is performed of whether the portable unit exists within a predetermined range outside from the vehicle or in the vehicle.
In the above-described conventional technique, the above-described search signal and response signal are the signals which include a different ID for each portable unit and various other signal parts, and are relatively long signals. Therefore, there has been a problem in that it takes too much time to perform the communication with all the portable units by exchanging individual search signals and response signals for individual portable units in sequence continuously until the communication is completed.